This invention is directed to an RF switch and in particular to an optoelectronic semiconductor switch.
The need for a switch which has a transmission bandwidth in excess of 100 MHz and an isolation of better than 70 dB is necessary for the successful implementation of a broadband communications service to subscribers. Fast-acting, reliable broadband switches are also required for communications satellites.
Coaxial switches can have an isolation of 60 dB or better over a frequency range of DC to 18 GHz, however their size is large compared to semiconductor switches and therefore these switches would not be practical in switching arrays. The RF PIN diode switch of the type described in the Hewlett Packard Application Note 929 is very fast and has an isolation in the order of 50 dB. However, the current required to maintain the "off" state of an PIN diode switch is of the order of 10 mA which is high for crosspoint switching matrices where most of the crosspoint switches are normally in the "off" state.
Another switch, the "Optoelectronic Cross-Point Switch" described in U.S. Patent application Ser. No. 017,722 filed on Mar. 5, 1979, by Elmer H. Hara and R. Ian MacDonald has a broad bandwidth and a high isolation factor, however, a significant amount of power is consumed maintaining the switch in the "off" state.